The invention relates to a hydraulic system used in an industrial vehicle, and in particular a materials handling vehicle or forklift truck. Examples of forklift trucks include reach trucks and turret trucks.
Forklift trucks are used in the transportation of goods and materials in a wide variety of applications. A fundamental characteristic of a forklift truck is the ability to lift and lower a load. Similarly, in order to improve efficiencies of transportation, additional load handling functions may be employed to adjust the position of the load after it has been raised. These functions, including lifting and lowering, are typically controlled by hydraulic systems that use hydraulic pressure that provides an operating force. The hydraulic system includes a pump and motor to generate the hydraulic pressure and corresponding hydraulic flow that operates mechanical devices performing the hydraulic functions.
An operator of the forklift truck is typically seated or standing in an operator cabin that includes any number of operator controls. Some of these operator controls control the hydraulic functions, including lifting and lowering the load. Other hydraulic functions may include side-shifting the load or tilting a mast, for example.
Hydraulic systems have a finite level of hydraulic fluid and hydraulic pressure that may be utilized in operating the hydraulic functions. For example, an available hydraulic fluid level may be limited by the size of a hydraulic reservoir. Similarly, the hydraulic pressure may be limited by the size of the hydraulic pump. Performance of the hydraulic functions can be reduced if the operator attempts to operate more than one hydraulic function at the same time, or the hydraulic system may instead restrict operation to one function at any given time. In either case, efficiencies of operation are negatively impacted.
The present invention addresses these and other problems associated with the prior art.